I. FIELD OF THE INVENTION
The invention relates to asphalt compositions containing i) an asphalt component, e.g., asphalt from vacuum bottoms or solvent-deasphalted bottoms and ii) an optional fluxing component, e.g., lube plant extract, and to a process for the improvement of their rheological properties. The invention further relates to modified asphalt compositions useful in a variety of applications, particularly paving asphalts, and to construction methods.
II. DESCRIPTION OF THE PRIOR ART
Solvent deasphalting (extraction of asphalts from heavy petroleum stocks) is a well-known petroleum process and is described in U.S. Pat. No. 3,951,781 to Owen (Mobil); U.S. Pat. No. 3,968,023 to Yan (Mobil); U.S. Pat. No. 3,972,807 to Uitti (UOP); U.S. Pat. No. 3,975,396 to Bushnell (Exxon); U.S. Pat. No. 3,981,797 to Kellar (UOP); U.S. Pat. No. 3,998,726 to Bunas (UOP); U.S. Pat. No. 4,017,383 to Beavon (Ralph M. Parsons); U.S. Pat. No. 4,054,512 to Dugan (Exxon); U.S. Pat. No. 4,101,415 to Crowley (Phillips); U.S. Pat. No. 4,125,458 to Bushnell (Exxon); and numerous others. Specific proprietary processes include the SOLVAHL solvent deasphalting process licensed by Institute Francais de Petrole, and the low-energy deasphalting process licensed by Foster Wheeler, U.S.A., shown schematically in FIG. 1. Deasphalting processes also include the ROSE supercritical fluid technology licensed by Kerr-McGee Corporation.
U.S. Pat. No. 5,601,697 to Miller et al. teaches SDA-produced asphalts (containing solvent deasphalting bottoms) made by blending SDA bottoms with aromatic extract. Preferably the extract is produced from an extraction process such as that employed in lubricating oil production. In one aspect, the asphalt can contain added polymers which can be vulcanized in situ with the asphalt by using sulfur and accelerators. No mention is made of the amount of sulfur added. The blending process produces asphalts of superior characteristics, e.g., PG64-22, which can meet the new Strategic Highway Research Program (SHRP) specifications for dynamic sheer, creep stiffness, and direct tension (tensile strength). As the new SHRP asphalt specifications impact the marketplace, particularly aided by the recent increases in federal funds for highway construction and repair, these new asphalt products will be particularly advantageous.
III. PROBLEMS PRESENTED BY PRIOR ART
At higher temperatures (58.degree. to 76.degree. C. (136.degree. to 169.degree. F.)), SDA-produced AC20 asphalts comprising lube plant extracts exhibit a higher potential for rutting according to SHRP testing when compared to asphalts produced by conventional means. The addition of lube plant extract produces a material which reacts to increased loading speeds more as an oil (Newtonian fluid) than as conventional asphalt (viscoelastic fluid). Conventionally-made asphalt enjoys a higher storage modulus, allowing it to store more energy from loading and thus preventing rutting from displacement. Accordingly, it would be advantageous to provide a way to modify the rheological properties of SDA-produced asphalt so as to improve its resistance to rutting at higher temperatures.
Sulfur has been used as a modifier for asphalt, by itself or with polymers, for vulcanization properties. U.S. Pat. No. 123,458 to Crawford discloses bituminous binders comprising asphalt, distilled coal tar, Crawford's redistilled oil and sulphur (2.2 wt %). U.S. Pat. No. 1,163,593 to Forrest describes a refining process for natural asphalts which prevents loss of naturally occurring sulfur found in crude oils which are refined to produce asphalt compositions. Hydrogen sulfide liberation is minimized by utilizing fixed oils to absorb sulfur. U.S. Pat. No. 1,266,261 to Henderson discloses premixing coal tar pitch and 6 to 14% sulfur in volatile petroleum and thereafter driving off the added petroleum. U.S. Pat. No. 1,353,003 to White, et al. describes acid- and alkali-resistant coatings containing coal tar pitch and crystallized sulfur which are prepared at low temperatures in order to prevent reaction of the pitch with sulfur. The sulfur is added to increase viscosity and reduce the melting point of the pitch. U.S. Pat. No. 3,739,853 to Kopvillem discloses sulfur addition to asphalt at 100% or more of asphalt content to produce an asphalt casting composition. U.S. Pat. No. 3,970,468 to Garrigues, et al. discloses sulfur emulsions in asphalt prepared by dispersion of 15 to 100 parts molten sulfur in 100 parts asphalt under high shear. U.S. Pat. No. 4,154,619 to Pronk describes the use of polysiloxane stabilizer for sulfur dispersed in bitumen. Sulfur is employed at levels of 20% to 50% of the bitumen and organosiloxane at 0.1% or less of bitumen. U.S. Pat. No. 4,211,575 to Burris discloses a process for producing asphaltic emulsions containing 10% to 50% sulfur, in the asphalt phase, utilizing a hydrocarbon solvent for softening. The sulfur is added to bitumen at temperatures below 152.degree. C. (305.degree. F.) to avoid evolving hydrogen sulfide. The composition is emulsified to produce an asphalt emulsion for pothole repair. U.S. Pat. No. 5,371,121 to Bellomy, et al. describes polymer-modified bitumen compositions which are mixtures of paving asphalt, styrene-butadiene block copolymer containing plasticizer oil, and 0.25% sulfur. U.S. Pat. No. 5,374,672 to Chaverot, et al. discloses an asphalt/polymer composition produced by mixing polymer, e.g., styrene and butadiene copolymer, with asphalt and then incorporating at 100.degree. C. to 230.degree. C. (220.degree. to 446.degree. F.) a sulphur-donating coupling agent in an amount suitable for providing an amount of elemental or radical sulphur representing 0.5 to 10% of the weight of the polymer. Canadian Patent No. 764,861 to Pethrick, et al. describes a bituminous composition containing i) propane precipitated asphalt which is sulfurized by the addition of 2 to 20 wt % of sulfur, ii) lube plant extract and iii) a vacuum residue. The vacuum residue is added to provide higher temperature susceptibility.
The prior art has utilized large amounts of sulfur (greater than 1 wt %) to make asphalts resistant to rutting. However, the addition of such amounts of sulfur can impart undesired brittleness resulting in premature failure of the asphalt in its use, e.g., as road surfaces.